The present invention generally relates to an apparatus and method for preventing particle contamination in a polishing machine that utilizes slurry for material removal and more particularly, relates to a method and apparatus for preventing particle contamination in a chemical mechanical polishing apparatus wherein a contamination prevention shield and a high pressure rinse apparatus cooperate to remove contaminated fluid from an interior region of the CMP housing.
An apparatus for polishing thin, flat semi-conductor wafers is well-known in the art. Such an apparatus normally includes a polishing head that carries a membrane for engaging and forcing a semi-conductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the ware and/or polishing head; a wafer unload station; or, a wafer load station.
More recently, a chemical-mechanical polishing (CMP) apparatus has been employed in combination with pneumatically actuated polishing head. The CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is xe2x80x9cplanarizedxe2x80x9d or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
A perspective view of a typical CMP apparatus as disclosed in U.S. Pat. No. 6,206,760 which is herein incorporated by reference is shown in FIG. 1A. The CMP apparatus 10 consists of a controlled mini-environmental 12 and a control panel section 14. In the controlled mini-environment 12, typically four spindles 16, 18, 20, 22 are provided (the fourth spindle 22 is not shown in FIG. 1A) which are mounted on a cross-head 24. On the bottom of each spindle, for instance, under the spindle 16, a polishing head 26 is mounted and rotated by a motor (not shown). A substrate such as a wafer is mounted on the polishing head 26 with the surface to be polished mounted in a face-down position (not shown). During a polishing operation, the polishing head 26 is moved longitudinally along the spindle 16 in a linear motion across the surface of a polishing pad 28. As shown in FIG. 1A, the polishing pad 28 is mounted on a polishing disk 30 rotated by a motor (not shown) in a direction opposite to the rotation al direction of the polishing head 26.
Also shown in FIG. 1A is a conditioner arm 32 which is equipped with a rotating conditioner disk 34. The conditioner arm 32 pivots on its base 36 for conditioning the polishing pad 38 for the in-situ conditioning of the pad during polishing. While three stations each equipped with a polishing pad 28, 38, 40 are shown, the fourth station is a head clean load/unload (HCLU) station utilized for the loading and unloading of wafers into and out of the polishing head. After a wafer is mounted into a polishing head in the fourth head cleaning load/unload station, the cross head 24 rotates 90xc2x0 clockwise to move the wafer just loaded into a polishing position, i.e., over the polishing pad 28. Simultaneously, a polished wafer mounted on spindle 20 is moved into the head clean load/unload station for unloading.
A cross-sectional view of a polishing station 42 is shown in FIGS. 1B and 1C. As shown in FIG. 1B, a rotating polishing head 26 which holds a wafer 44 is pressed onto an oppositely rotating polishing pad 28 mounted on a polishing disc 30 by adhesive means. The polishing pad 28 is pressed against the wafer surface 46 at a predetermined pressure. During polishing, a slurry 48 is dispensed in droplets onto the surface of the polishing pad 28 to effectuate the chemical mechanical removal of materials from the wafer surface 46.
An enlarged cross-sectional representation of the polishing action which results from a combination of chemical and mechanical effects is shown in FIG. 1C. The CMP method can be used to provide a planar surface on dielectric layers, on deep and shallow trenches that are filled with poly silicon or oxide, and on various metal films. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An outer layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing, a metal oxide layer can be formed and removed repeatedly.
During a CMP process, a large volume of a slurry composition is dispensed. The slurry composition and the pressure applied between the wafer surface and the polishing pad determine the rate of polishing or material removal from the wafer surface. The chemistry of the slurry composition plays an important role in the polishing rate of the CMP process. For instance, when polishing oxide films, the rate of removal is twice as fast in a slurry that has a PH of 11 than with a slurry that has a pH of 7. The hardness of the polishing particles contained in the slurry composition should be about the same as the hardness of the film to be removed to avoid damaging the film. A slurry composition typically consists of an abrasive component, i.e., hard particles and components that chemically react with the surface of the substrate. For instance, a typical oxide polishing slurry composition consists of a colloidal suspension of oxide particles with an average size of 30 nm suspended in an alkali solution at a pH larger than 10. A polishing rate of about 120 nm/min can be achieved by using this slurry composition. Other abrasive components such as ceria suspensions may also be used for glass polishing where large amounts of silicon oxide must be removed. Ceria suspensions act as both the mechanical and the chemical agent in the slurry for achieving high polishing rates, i.e., larger than 500 nm/min. While ceria particles in the slurry composition remove silicon oxide at a higher rate than do silica, silica is still preferred because smoother surfaces can be produced. Other abrasive components, such as alumina (Al3O2) may also be used in the slurry composition.
A slurry composition is a material that easily accumulates after contacting dry air or without proper circulation of air. When slurry is left on the surface of the process environment, i.e., on the surface of the spindles or the conditioner arms in a CMP machine, it will dry a and accumulate to become a source of particle contamination for the wafers that are processed in the polishing housing interior. Slurry particles can easily fall from moving parts to the polishing pad due to mechanical vibration of the CMP apparatus to cause macro-scratch of the wafer surface. Slurry particles may also become source of particle contaminants for the wafer surface and for the CMP housing interior environment. It is therefore highly desirable that particle contaminants resulting from dry slurry to be avoided or eliminated.
Referring now to FIG. 1D, wherein a simplified plane view of a conventional CMP apparatus 50 is shown. In the apparatus 50, a CMP housing interior 52 houses a cross member 54 equipped with four spindles (not shown). Two spindle clean modules 56, 58 are positioned adjacent to the spindle positioned in the lower corner.
A plan view of a conventional CMP apparatus 50 is shown in FIG. 1E illustrating a conditioner arm 62. The conditioner disc 90 and conditioner arm 62 are cleaned by conventional methods to remove any slurry deposits splattered thereon during the chemical mechanical polishing process. Polishing pads 82, 84, and 86 are also shown in FIG. 1E without the spindle in place. It should be noted that for each of the polishing pad positions, e.g., for each of 82, 84, and 86, a conditioner arm 62 is utilized for the in-situ conditioning of the respective polishing pads.
A detailed perspective view of the conditioner arm 62 and the conditioner disc 90 resting in a conditioner clean cup 88 is shown in FIG. 2D. It is seen that slurry deposits 70 have cumulated on the top horizontal surface 92 of the conditioner disc 90. Conventional means for removing the slurry deposits from the conditoner disc include spraying deionized water from the bottom of the chamber.
FIG. 1G illustrates a conditioner arm shield used in the prior art. The housing wall has a portion that protrudes outwardly and allows the conditioner arm to rest therewithin. However, the conditioner arm shield of the prior fails to protect against a slurry accumulation on the inner walls of the housing and did not adequately prevent a slurry accumulation from accumulating on the conditioner arm pad.
The prior art allows for the slurry to splash on the skin cover during pad conditioning and during processing. The slurry also condenses on an inner portion of the housing wall 100 and becomes a solid small powder that often drops onto the pad. These slurry powder particles cause scratching of the wafer during processing and monitoring.
The deionized water also leaks between the inner surf ace of the middle skin and the CMP machine during a high pressure rinse. The middle skin of the prior art is made from a glass material that is very heavy and cracks or breaks easily. Also, access to the middle skin is difficult making it difficult to perform preventative maintenance on the skin or clean the inner wall.
The present invention provides a new stronger shield that avoids water leakage; and provides a water flow system adapted for use with the new shield to reduce slurry condensation on the CMP machine.
It is therefore an object of the present invention to provide a method for preventing particle contamination in a CMP apparatus that does not have the drawbacks or shortcomings of the conventional methods for preventing particle contamination in a CMP apparatus.
It is another object of the present invention to provide a method for preventing particle contamination in a CMP apparatus that utilizes a cleaning solvent to prevent the formation of particles from the slurry composition.
It is a further object of the present invention to provide a method for performing a high pressure rinse for preventing particle contamination in a CMP apparatus by providing a fluid conduit and a plurality of spray nozzles in the polishing CMP housing interior for the cleaning of dried slurry that was splattered on the machine surface and the interior wall of the CMP apparatus housing.
It is another further object of the present invention for preventing particle contamination of the interior housing wall of a housing for a CMP apparatus by providing a contamination prevention shield for directing flow of fluid from a high pressure rinse cycle away from the interior wall of the housing.
It is yet another object of the present invention to provide a plurality of contamination prevention shields juxtaposed between each spindle and conditioner arm and the housing wall for directing flow of cleaning solvent sprayed to remove slurry deposits on the components during a high pressure rinse.
It is still another further object of the present invention to provide a contamination prevention shield that is water resistent, lighweight, easily removable and does not easily shatter or crack.
In accordance with the present invention, an apparatus and method for preventing particle contamination in a polishing machine such as a chemical mechanical polishing apparatus are provided.
In a preferred embodiment, a contamination prevention apparatus for preventing contamination of a CMP apparatus is disclosed. The CMP apparatus is of the type having a conditioner arm and a housing having a planer wall having a top peripheral edge, an outer sidewall, an inner side wall, and a lower peripheral edge and wherein the planer wall further has an opening disposed. The contamination prevention apparatus further has:
(a) a contamination prevention shield having a cleaning cup, two vertical side shields, a front vertical shield, and a floor that cooperate to prevent leakage of fluid splattered during a high pressure rinse of the CMP apparatus and an interior portion of the housing; and
(b) a high pressure rinse apparatus connected to the contamination prevention shield having a conduit further connected to a fluid flow source wherein the conduit has at least one nozzle disposed within for dispensing cleaning fluid during a high pressure rinse cycle.
The present invention is further directed to:
(a) a plurality of contamination prevention shields each having a cleaning cup, two vertical side shields, a front vertical shield, and a floor, wherein each contamination prevention shield is juxtaposed between the inner side wall and the CMP apparatus, and wherein each contamination prevention shields cooperate to prevent leakage of fluid splattered during a high pressure rinse of the CMP apparatus and an interior portion of the housing; and
(b) a high pressure rinse apparatus connected to the contamination prevention shield having a conduit connected to a fluid flow source wherein the conduit has a plurality of spaced-apart nozzles disposed within for dispensing cleaning fluid during a high pressure rinse cycle. Additionally, a method of use for several embodiments of the present invention is disclosed herein.